Dishwasher door operator

ABSTRACT

A dishwasher having a washing chamber includes a vertically slidable door for selectively opening and closing the washing chamber. A shaft is positioned on the dishwasher for rotation on a vertical axis. A linear actuator positioned on the shaft moves linearly along the shaft when the shaft is rotated. The linear actuator is connected with the door so that movement of the actuator is imparted to the door. A reversible drive motor selectively rotates the shaft in first and second opposite directions to selectively move the linear actuator up and down the shaft and effect opening and closing of the door. Automatic control is provided to effect automatic opening of the door at the end of a washing cycle in the dishwasher.

United States Patent 2,614,020 10/1952 Collins lnventor Appl. No.

Filed Patented Assignee DISHWASHER noon OPERATOR 10 Claims, 9 Drawing Figs.

US. Cl.

rm. Cl

A47b 88/00 Field of Search References Cited UN lTED STATES PATENTS Primary Examiner.lames T. McCall Attorney-Meyer, Tilberry and Body ABSTRACT: A dishwasher having a washing chamber includes a vertically slidable door for selectively opening and closing the washing chamber. A shaft is positioned on the dishwasher for rotation on a vertical axis. A linear actuator positioned on the shaft moves linearly along the shaft when the shaft is rotated. The linear actuator is connected with the door so that movement of the actuator is imparted to the door. A reversible drive motor selectively rotates the shaft in first and second opposite directions to selectively move the linear actuator up and down the shaft and effect opening and closing of the door. Automatic control is provided to efiect automatic opening of the door at the end of a. washing cycle in the dishwasher.

PATENTEDJUHZQISYI 3,589.78?

sum 1 OF 3 IN VENTOR. EUGENE ME SSE RS'M/ TH ATTORNEYS PATENTED JUN29 as?! SHEU 2 OF 3 INVENTOR. EUGENE MESSE RSM/ T H ATTORNEYS PATENTEUJuN29|9n 3,589,787

sum 3 OF 3 INVENTOR.

EUGENE MEISSERSM/TH I ATTORNEYS DISHWASHER DOOR OPERATOR BACKGROUND OF THE INVENTION This application pertains to the art of dishwashers and more particularly to dishwashers having vertically slidable doors for selectively opening and closing a washing chamber. The in vention is particularly applicable to commercial type dishwashers and will be described with particular reference thereto although it will be appreciated that the invention has broader applications and may be used with other types of dishwashers.

Commercial dishwashers commonly have at least one vertically slidable door for selectively opening and closing a washing chamber. In previous dishwashers of this type, hydraulic or mechanical mechanisms have been proposed for opening and closing the door. In such prior arrangements, the door operating mechanism exerted a large force in closing the door so that damage could be caused if a person's arm were accidentally beneath the door when it closed. In addition, previous door openers for dishwashers have been very complex.

SUMMARY OF THE INVENTION In accordance with the present invention, a dishwasher having a washing chamber is provided with a vertically slidable door for selectively opening and closing the washing chamber. In a preferred arrangement, the door is at a side of the machine. A device for selectively opening and closing the door includes a vertical axis shaft rotatably mounted at the rear of the dishwasher. A linear actuator is positioned on the shaft for linear movement thereon when the shaft is rotated. A reversible drive motor is provided for selectively rotating the shaft in first and second opposite directions to selectively move the linear actuator up or down the shaft. The linear actuator is connected with the door so that linear movement of the actuator on the shaft is imparted to the door for selectively raising or lowering the door. In the preferred arrangement, the liner actuator comprises a plurality of rollers spring biased into engagement with the shaft. When the shaft is rotated, the rollers roll in contact with the shaft along helical paths so that the linear actuator moves up or down the shaft depending on which direction the shaft is being rotated. Spring biasing the rollers into engagement with the shaft limits the amount of linear thrust the actuator can provide. Resistance to movement of the door and actuator will simply cause the rollers to slip in place on the shaft. Therefore, if a person has his arm in the washing chamber of a dishwasher and the door is moving downward, the rollers will simply slip in place on the shaft when the door contacts a person's arm so that no damage will be done. In the preferred arrangement, counterbalancing springs are connected with the door to reduce the lifting force required for opening of the door. With such an arrangement, the linear lifting force required of the linear actuator may be minimized so that minimum thrust is provided when the door is closing and the rollers will simply slip on the shaft if the door strikes something in closing. In accordance with the invention, an interlock arrangement is provided with the control of the dishwasher so that the linear actuator is energized to open the door automatically at the end of a washing cycle. In addition, an interlock with the dishwasher controls is provided so that washing cannot take place unless the door is closed.

It is a principal object of the present invention to provide a vertically slidable dishwasher door with a power-driven device for effecting opening and closing movement of the door.

It is a further object of the present invention to provide such a dishwasher door operator which is simple and economical to manufacture, and is very reliable in operation.

It is also an object of the present invention to provide such a dishwasher door operator which exerts a limited downward force on the door.

It is an additional object of the present invention to provide such a dishwasher door operator which is automatically energized at the end of a dishwasher washing cycle to effect opening movement of the door.

BRIEF DESCRIPTION OF THE DRAWING The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof.

FIG. 1 is a front, elevational view of a dishwasher having the present invention incorporated therein and with portions cut away for clarity of illustration;

FIG. 2 is a side, elevational view looking in the direction of arrows 2-2 of FIG. 1 and with portions cutaway for clarity of illustration;

FIG. 3 is a cross-sectional view looking in the direction of arrows 3'3 of FIG. 2;

FIG. 4 is a cross-sectional view looking in the direction of arrows 4-4'of FIG. 2;

FIGfS-is a rear,=elevational view looking in the direction of arrows 5-5 of'FIG. 4 v

FIG. 6 is a plan view looking in the direction of arrows 6-6 of FIG. 5;

FIG. 7 isa cross-sectional, elevational view looking in the direction of arrows 7-7 of FIG. 6; r 1

FIG. 8 is a side, elevational view similar to FIG. 2 and show ing the door in an elevated position; and

FIG. 9 is a schematic electrical diagram showing a portion of a control arrangement for use with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, wherein the showings are for purposes of illustrating the preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows dishwasher A having the present invention incorporated therein. Dishwasher A includes a front panel 12 and corner angle members 14 which also serve as supporting legs for dishwasher A; A bottom frame member 16 is provided, and is connected with angle members 14 for supporting various components of the dishwasher mechanism. Water main 18 is connected to dishwasher A and leads either to washing liquid sump 20 through solenoid valve 22, or to rinse water headers 24 and 26 through solenoid valve 28. Washing liquid sump 20 is connected with a motor pump unit 30 through con-. duit 32, and motor pump unit 30 is mounted on a suitable support 34 secured to bottom frame member 16. Motor pump unit 30 includes a discharge conduit 36 leading to spray nozzles on washing headers 38 and 40.

Dishwasher A includes a washing compartment 42 having a bottom grid 44 on which a basket 46 may be supported. In operation of the device, water will be fed to washing liquid sump 20 by opening of solenoid valve 22. When sufficient water is in sump 20, solenoid valve 22 will be closed. Motor pump unit 30 will then operate to send washing liquid through suitable spray nozzles on washing headers 38 and 40. Articles positioned in basket 46 will then be washed clean of dirt. At the end of the washing cycle, motor pump unit 30 is shut off while another suitable solenoid valve opens discharge outlet 48 in washing liquid sump 20 to drain washing liquid therefrom. Solenoid valve 28 is also then opened to feed hot clean rinse water'through suitable spray nozzles on rinsing headers 24 and 26. At the end of the rinsing cycle, solenoid valve 28 will close. v

The washing cycle of dishwasher A is started and controlled by a suitable timer 50 having an actuating knob 51. This operation of a dishwasher of this type is well known and conventional in the dishwasher art. When a washing cycle is referred to in this specification, it will be understood that those words mean the entire washing, rinsing and drying cycle of the dishwasher.

In accordance with the invention, dishwasher A is provided with a front defined by front panel 12, a rear which is oppositely disposed front panel 12, and opposite sides. The opposite sides of dishwasher A include vertically slidable doors 52 which are selectively slidable up and down to selectively open and close washing chamber 42. As best shown in FIG. 4, vertically elongated channel members 56 are secured to an inner face of angle members 14 as by welding, and to edge portions of front panel 12 and rear panel 58 as by welding. The vertical edge portions of doors 52 are received in channels 56 for vertical sliding movement therein. Suitable seals may be provided to prevent leakage of liquid from the washing chamber in a well known manner. Another pair of vertically elongated channel members 60 are secured to angle members 14 adjacent rear panel 58. Another pair of channel members 62 are secured to a U-shaped member 64 which includes a pair of spaced-apart arms 66. Channels 60 and 62 each have one of their flanges received in the U-shaped opening of the other channel so that channels 62 and U-shaped member 64 are vertically slidable up and down relative to channels 60. Arms 66 of U-shaped member 64 are secured to doors 52 as by pins 68.

A reversible electric motor 70 is mounted on a suitable support 72 attached to bottom frame member 16 of dishwasher A. Motor 70 includes a power takeoff shaft, having a pulley 74 thereon. At the rear of dishwasher A, a vertical axis tubular shaft 76 is rotatably mounted in a bottom bearing 78. The bottom end of shaft 76 has a pulley 80 thereon which is drivingly connected with pulley 74 of motor 70 as by a belt 82. Shaft 76 is substantially centrally located along the front to rear centerline of dishwasherA intermediate the sides thereof as defined by doors 52. A linear actuator 84 is positioned on shaft 76 and defines an upper bearing for shaft 76. Linear actuator 84 is connected with channels 62 so that vertical up and down movement of actuator 84 on shaft76 also imparts similar movement to channels 62 and U-shaped member 64. Arms 66 of U-shaped member 64 being connected with doors 52, the up and down movement is also imparted to doors 52.

In the preferred arrangement, doors 52 are provided with counterbalancing springs for reducing the weight which must be lifted by linear actuator 84 in opening doors 52. In one arrangement, the counterbalancing arrangement may be defined by a pair of channels 86 pivotally attached as at 88 adjacent the rear of dishwasher A. Doors 52 include a roller 90 rotatably mounted on a stud 92 welded to the outer face of doors 52. Roller 90'is received in channel member 86 as shown in FIG. 3. Suitable brackets 94 adjacent the bottom rear of dishwasher A have hooked ends 96 of springs 98 at- 1 tached thereto. Springs 98 are connected with channel 86 by rods 102. Springs 98 act on channel 86 to pivot channels 86 clockwise as viewed in FIG. 2 about pivot point 88. This force is imparted to doors 52 by channels 86 contacting rollers 90. In one arrangement, the weight of doors 52 is sufficient to move doors 52 vertically downward to their closed position against the force of springs 98. However, it will be recognized that springs 98 may be powerful enough to raise doors 52 so that closing movement of doors 52 to their completely closed position is effected by linear actuator 84 providing downward thrust to doors 52 against the bias of springs 98.

As shown in FIG. 5, linear actuator 84 is connected with a laterally extending member 106 which is also secured to channels 62. Channels 60 and 62 cooperate with one another to define guideways for movement of U-shaped member 64 and lateral member 106, with linear actuator 84 positioned intermediate channels 62 on shaft 76 as shown in FIG. 5.

In the preferred arrangement, linear actuator 84 includes rear and front halves I08 and 110. Rear half 108 is secured to lateral member 106 as by bolts 112 extending through suitable bores in lateral member 106 and threaded into threaded bores in rear half 108. Front half 110 of linear actuator 84 includes enlarged bores 114 intersecting smaller diameter bores 118. The intersections between large bores 114 and small bores 118 defines shoulders. Coil springs 116 positioned in bores 114 act against such shoulders at one end and against the heads of bolts 120 at their other ends. Bolts 120 freely extend through bores 114 and 118, and through coil springs 116, to threaded engagement in bores 122 of rear half 108. The heads of bolts 120 are smaller than the diameter of large bores 114 so that the heads of bolts 120 may enter bores 114. Bolts 120 may be tightened and loosened to vary the force with which coil springs 116 bias from half toward rear half 108 of linear actuator 84.

Each half 108 and 110 of linear actuator 84 is provided with upper and lower recesses as shown at 126 and 128 with respect to half 108 in FIG. 7. It will be understood that front half 110 is similarly formed. Recesses 126 and 128 are connected by a groove 130 through which shaft 76 freely extends. The bottom portions of recesses 126 and 128 are provided with nonvertical bores 132 for receiving shaft 134. Shafts 134 may have their ends threaded for reception in bores 132 or may be press fit therein. Rollers 136 are rotatably mounted on shafts 134 and engage shaft 76. Roller shafts 134 are nonvertical and intersect shaft 76 at angles so that the periphery of rollers 136 roll in contact with shaft 76 over helical paths when shaft 76 is rotated. It will be recognized that the force with which rollers 136 engage shaft 76 may be varied by adjusting bolts 120 to vary the force with which coil springs 116 bias front half 110 of linear actuator 84 toward rear half 108. When shaft 76 is rotated, rollers 136 will roll in contact with shaft 76 on helical paths so that linear actuator 84 will move up or down shaft 76 depending upon the direction of rotation thereof. This linear movement of linear actuator 84 along shaft 76 will be imparted to doors 52 through lateral member 106, channels 62 and U-shaped member 64. Doors 52 are shown in their open position in FIG. 8 with linear actuator 84 approaching the top end of shaft 76. When movement of doors 52 is resisted by the doors striking an object, the frictional engagement between rollers 136 and shaft 76 will become insufficient to allow rollers 136 to move in helical paths along shaft 76 so that rollers 136 and linear actuator 84 will merely slip in place on shaft 76. This is a very important feature of the present invention as during closing movement of doors 52 the arm of an operator may be positioned within washing chamber 42. Contact of the lower edge of doors 52 with a persons arm or something else will simply cause linear actuator 84 to slip in place on shaft 76 and the force exerted by the bottom edge of a door 52 against a persons arm will be so small that no injury can be caused. In this regard, counterbalancing springs 98 are very important to minimize this downward force. For example, linear actuators 84 would normally have to grip shaft 76 with sufficient force to raise the entire weight of doors 52 and associated parts defined by U shaped member 64 on channel 62. However, providing counterbalancing springs 98 reduces the amount of force required by linear actuator 84 to raise doors 52 to their open position. With this arrangement, the downward force exerted by linear actuator 84 on doors 52 is also minimized and may be kept low enough so that injury will not be caused if an operator has his arm in washing chamber 42 when doors 52 are closed. It will also be recognized that counterbalancing springs 98 may be made powerful enough to normally open doors 52 so that linear actuator 84 positively moves doors 52 to their lower closed position against the biasing force of springs 98. With such an arrangement, the force required of linear actuator 84 is very minimal and actuator 84 will readily slip in place on shaft 76 when resistance to movement of doors 52 is encountered.

In accordance with one arrangement, a control circuit for operation of dishwasher A and doors 52 may be provided as shown in FIG. 9. With this arrangement, motor 70 for driving shaft 76 to raise and lower doors 52 may be a universal motor provided with a four-pole double-throw switch RS1. Poles 140, 142, 144 and 146 are cross-connected by wires 148 and 150 as shown in FIG. 9. That is, wire 148 cross-connects pole 142 with pole 146 while wire 150 cross-connects pole with pole 144. When switch RS1 is thrown so that contacts 140 and 152, and contacts 142 and 154 are connected, current will flow from bottom to top, as viewed in FIG. 9, through the armature winding of motor 70 after flowing through field winding 156. On the other hand, when switch RS1 is thrown so that contacts 146 and 152, and contacts 144 and 154 are connected, current will flow from top to bottom, as viewed in FIG. 9, through the armature winding of motor 70 so that motor 70 will rotate in a reverse direction. Through this arrangement, the rotational direction of shaft 76 is selectively reversed to move linear actuator 84 selectively up or down shaft 76. In operation of the circuit, manual rotation of knob 51 for timer 50 of FIG. 1 will close switch TSl. With doors 52 in their raised position of FIG. 8, switch LS1 is in the full line position shown in FIG. 9, and reversing switch RS1 is in a position in which motor 70 will rotate shaft 76 to move linear actuator 84 downward. Therefore, doors 52 move downward until reaching their closed position at which time switch operators on the door operating mechanism move switch LS1 to the dotted line position shown in FIG. 9 and also actuate reversing switch RSI to reverse the connections to motor 70. Current then flows through switches TS] and LS1 to timer 50 while current is cut off to motor 70. Timer 50 then operates through the entire washing, rinsing and drying cycle of dishwasher A by selectively opening and closing suitable solenoid valves and operating motor pump 30. At the end of the operating cycle of dishwasher A, timer 50 closes switch TS2 and opens switch TSI. Therefore, current will flow from source 158 through switch T82 and normally closed switch LS2 to motor 70. Reversing switch RS1 having been actuated when doors 52 were closed, motor 70 will now rotate in a reverse direction to rotate shaft 76 in a direction for moving linear actuator 84 upward to raise doors 52 to their open position. Upon doors 52 reaching their full open vertical position, a trip arm on the door operator will open switch LS2 so that current will be cut off to motor 70. With switch TSI already having been opened at the end of the operating cycle of dishwasher A, and switch LS2 opened upon doors 52 reaching their vertical upward position, everything is deenergized. Upon initial upward movement of doors 52, switch LS1 will again have moved to its full line position shown in FIGURE 9. Therefore, rotation of knob 51 of timer 50 to its starting position once again will close switch TSl while opening switch TS2 so that dishwasher A will go through another operating cycle.

In one arrangement for operation of the circuit of FIGURE 9, U-shaped member 64 and lateral member 106 have switchactuating arms 162 and 164 for operating reversing switch RS1 as shown in FIGURE 5. Lateral member 106 is also provided with switch actuating arms 166 and 168 for switches LS1 and LS2 respectively. With doors 52 in their downward closed position, actuating arm 166 will hold switch LS1 in the dotted line position shown in FIGURE 9 to provide current flow to timer 50. Switch LS2 will be closed, whilereversing switch RS1 will be thrown so that motor 70 would rotate shaft 76 in a direction to move linear actuator upwardly when current is supplied to motor 70. At the end of the operating cycle,

switch TS2 will close to provide current to motor 70 through switch LS2. Doors 52 and lateral member 106 will then begin moving upwardly and actuator 166 will move away from switch LS1 so that switch LS1 will return to its full line position in FIGURE 9. Upon doors 52 reaching their vertical upward open position, actuator 168 will open switch LS2 while actuator 164 will operate switch RS1 for reversing connections to motor 70. In this condition, everything in the circuit will be open. For another operating cycle of dishwasher A, an operator will move knob 51 of timer 50 to its on position in which switch TS] is closed and switch T82 is open. Current will then flow to motor 70 through switches T51 and LS1. Upon doors 52 reaching their downward closed position, actuator 166 on lateral member 106 will move switch LS1 to the dotted line position shown in FIGURE 9 while actuator 162 on U-shaped member 64 will simultaneously operate reversing switch RSI to reverse connections to motor 70. Timer 50 will then go through the operating cycle of dishwasher A until switch T51 is opened and switch T82 is closed. Current will then be provided through switches T52 and LS2 to motor 70 and motor 70 will rotate in a reverse direction because switch RS2 had been reversed when doors 52 reached their downward position. Doors 52 will then automatically move upward until reaching their full open position at which time switch LS2 will again be opened to deenergize motor 70. It

will be recognized that this arrangement provides an automatic door opening operation at the end of an operating cycle of dishwasher A. In addition, the interlocking arrangement between the operator for doors 52 and the control device for the dishwasher prevents operation of dishwasher A unless doors 52 are in their fully closed position. Therefore, it is not possible to cause injury to an operator who may have his arm within washing chamber 42 because the washing cycle of dishwasher A cannot be energized until doors 52 are fully closed.

It will be recognized that shaft 76 may also be driven by motor pump 30. For example, motor pump 30 may be reversible and be connected with shaft 76 through a solenoid operated clutch. When motor pump 30 is operated to transfer washing liquid from sump 20 to headers 38 and 40, no torque will be transferred to shaft 76 through the solenoid operated clutch. However, during beginning upward or downward movement, when there is no liquid in sump 20, the solenoid clutch may be energized to transfer torque to shaft 76 from motor pump unit 30.

While the invention has been described with reference to a preferred embodiment, it is obvious that modifications and alterations will occur to. others upon the reading and understanding of this specification.

Having thus describedmy invention, I claim:

1. A dishwasher having a washing chamber, vertically slida ble door means for selectively opening and closing said washing chamber, vertical shaft means rotatably mounted on said dishwasher, linear actuator means positioned on said shaft for linear movement along said shaft during rotation of said shaft, connecting means connecting said linear actuator with said door means, and reversible drive means for selectively rotating said shaft means in first and second opposite directions to selectively move said linear actuator means up and down said shaft means to effect opening and closing of said door means.

2. The dishwasher of claim 1 wherein said linear actuator means comprises a plurality of rollers resiliently biased into engagement with said shaft means around the periphery thereof, said rollers being rotatable on nonvertical axes for rolling in helical paths along said shaft during rotation of said shaft.

3. The dishwasher of claim 2 and further including counter balancing means connected with said door means for decreasing the weight thereof and reducing the linear force required from said linear actuator means to move said door means upward.

4. The dishwasher of claim 1 and further including control means for controlling an operating cycle of said dishwasher, and automatic activating means for activating said drive means to rotate said shaft means and move said door means to an open position at the end of said operating cycle.

5. The dishwasher of claim 4 and further including deactivating means for deactivating said drive means when said door means reaches its fully open position.

6. The device of claim 5 and further including interlock means for preventing operation of said control means when said door means is in an open position, and automatic operating means for overriding said interlock means to render said control means operative when said door means is in its closed position.

7. The dishwasher of claim I wherein said dishwasher includes a front, a rear and opposite sides, said door means comprising a pair of doors, one of said pair of doors being vertically slidable for selectively opening and closing each of said opposite sides, said shaft means being positioned on said rear of said dishwasher and substantially centrally located between said opposite sides.

8. The dishwasher of claim 7 wherein said connecting means connecting said linear actuator means with said pair of doors comprises a substantially U-shaped member having a pair of spaced-apart parallel arms connected by a bottom portion, one of said arms being attached to each of said doors.

9. The device of claim 8 and further including spaced-apart guide means for slidably guiding said U-shaped member for slipping relative to said shaft, and further including counterbalancing means connected with said door means for reducing the weight thereof and rendering said limited linear thrust sufficient to lift said doors upwardly. 

1. A dishwasher having a washing chamber, vertically slidable door means for selectively opening and closing said washing chamber, vertical shaft means roTatably mounted on said dishwasher, linear actuator means positioned on said shaft for linear movement along said shaft during rotation of said shaft, connecting means connecting said linear actuator with said door means, and reversible drive means for selectively rotating said shaft means in first and second opposite directions to selectively move said linear actuator means up and down said shaft means to effect opening and closing of said door means.
 2. The dishwasher of claim 1 wherein said linear actuator means comprises a plurality of rollers resiliently biased into engagement with said shaft means around the periphery thereof, said rollers being rotatable on nonvertical axes for rolling in helical paths along said shaft during rotation of said shaft.
 3. The dishwasher of claim 2 and further including counter balancing means connected with said door means for decreasing the weight thereof and reducing the linear force required from said linear actuator means to move said door means upward.
 4. The dishwasher of claim 1 and further including control means for controlling an operating cycle of said dishwasher, and automatic activating means for activating said drive means to rotate said shaft means and move said door means to an open position at the end of said operating cycle.
 5. The dishwasher of claim 4 and further including deactivating means for deactivating said drive means when said door means reaches its fully open position.
 6. The device of claim 5 and further including interlock means for preventing operation of said control means when said door means is in an open position, and automatic operating means for overriding said interlock means to render said control means operative when said door means is in its closed position.
 7. The dishwasher of claim 1 wherein said dishwasher includes a front, a rear and opposite sides, said door means comprising a pair of doors, one of said pair of doors being vertically slidable for selectively opening and closing each of said opposite sides, said shaft means being positioned on said rear of said dishwasher and substantially centrally located between said opposite sides.
 8. The dishwasher of claim 7 wherein said connecting means connecting said linear actuator means with said pair of doors comprises a substantially U-shaped member having a pair of spaced-apart parallel arms connected by a bottom portion, one of said arms being attached to each of said doors.
 9. The device of claim 8 and further including spaced-apart guide means for slidably guiding said U-shaped member for vertical upward and downward movement, said linear actuator means being positioned intermediate said guide means.
 10. The dishwasher of claim 9 wherein said linear actuator means is capable of supplying limited linear thrust before slipping relative to said shaft, and further including counterbalancing means connected with said door means for reducing the weight thereof and rendering said limited linear thrust sufficient to lift said doors upwardly. 